1. Field of the Invention
The present invention relates generally to integrated circuit packaging and, more particularly, to a method for attaching an integrated circuit die to a leadframe or substrate.
2. Background of the Related Art
This section is intended to introduce the reader to various aspects of art which may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The packaging of electrical circuits is a key element in the technological development of any device containing electrical components. A single integrated circuit die is typically encapsulated within a sealed package to be mounted on a printed circuit board (PCB) or a similar apparatus for incorporation into a system. The integrated circuit die is generally encapsulated within a molding compound to protect the die from external contamination or physical damage. Because the integrated circuit die is generally encapsulated, the encapsulated integrated circuit package must typically also provide a system of interconnects for electrically coupling the integrated circuit die to a PCB or other external circuitry.
Two common surface mount techniques are using lead-on-chip (LOC) and board-on-chip (BOC) packaging. For LOC packages, an integrated circuit die is typically attached to a leadframe. A leadframe is a metal frame comprised of a plurality of lead fingers. The integrated circuit die is physically attached to the lead fingers by an adhesive, such as tape or epoxy. Prior to the encapsulation process, the adhesive material is disposed onto the die, and the die is mounted to the lower surfaces of the lead fingers. The lead fingers are electrically coupled to the integrated circuit die by bond wires which extend from the lead fingers to pads along the center of the integrated circuit die. The leadframe package is then encapsulated such that the lead fingers extending from the integrated circuit die protrude from the edges of the molding compound used to encapsulate the module. A molded package is then excised from the leadframe resulting in an encapsulated integrated circuit die with lead fingers extending outside of the molding compound to electrically couple the integrated circuit die to a PCB or other electrical device.
For BOC packages, the integrated circuit die is attached to a substrate. The integrated circuit die is mounted on the substrate “face-down.” In this instance, the substrate contains a slot. Since the integrated circuit die is mounted face-down, the bond pads on the surface of the integrated circuit die are arranged to correlate with the slot opening in the substrate. Bond wires are attached from the bond pads on the integrated circuit die to the backside of the substrate. The substrate contains conductive traces to distribute electrical signals to pads along the backside of the substrate which will eventually be attached to a PCB or other external device.
Alternately, the integrated circuit die may be attached to the substrate “face-up”. That is to say that the side of the integrated circuit die containing the bond pads for wire bonding the integrated circuit die to the substrate are left exposed on the top surface. This is known as chip-on-board or COB packaging. The backside of the integrated circuit die, i.e., the side not containing the bond pads, is adhered to the substrate. In a COB package, bond wires are attached from the surface of the integrated circuit die down to pads on the surface of the substrate. The substrate contains conductive traces which route signals from the top side of the substrate to the backside of the substrate.
Regardless of whether the integrated circuit die is mounted to the substrate face-up (COB) or face-down (BOC), either the die or the substrate is generally disposed with an adhesive, such as tape or epoxy, to attach the die to the substrate. Finally, the entire package is generally encapsulated in a molding compound. Various techniques, such as a pin grid array (PGA) or a ball grid array (BGA), may be incorporated to provide a means of connecting the integrated circuit package to the PCB or other external device.
Regardless of whether LOC or BOC/COB packaging technology is incorporated, a key component in the packaging process is the attachment of the integrated circuit die to the leadframe (LOC) or substrate (BOC/COB). One means of attaching the integrated circuit die to the leadframe or the substrate is to cover the die or substrate (BOC/COB) with an adhesive tape. For LOC packages, one or two solid strips of tape are disposed on the topside of the die to facilitate attachment to the leadframe. For BOC/COB packages, one or two solid strips of adhesive tape may be disposed on the die or the substrate in order to facilitate the attachment of the die to the substrate. Typically, the attachment of the die to the leadframe or substrate creates the biggest reliability issues in package yield. Pressure created by temperature variation, moisture sensitivity and thermal exposure often causes die attach failures. Thus, a method and apparatus for attaching the integrated circuit die to a leadframe or substrate which reduces the likelihood of package failure due to die attach failure would be desirable.
The present invention may address one or more of the problems set forth above.